Wheat, corn, oats, barley and related grains are major crops raised for both human and animal consumption. Such crops are becoming increasingly important energy sources. Since the amount of world-wide grain production becomes more critical as total population expands and as natural energy sources diminish, novel methods for increasing crop yields are constantly being sought.
One of the major problems with growing grain crops in certain sections of the world is the lack of sufficient water. Irrigation in such areas generally is impossible, and total yearly rainfall is customarily insufficient in such areas to permit the growing of crops every year on the same land. Accordingly, one practice commonly followed in areas receiving a sparcity of rainfall is to allow the land to lie fallow during alternate years. The practice of a fallow land program requires that the land remain unplanted during the year following the harvest of a crop. Such practice permits the accumulation and conservation of the available soil moisture, and thus permits the growth of a grain crop in the growing season following the fallow period.
One of the primary problems with fallow land programs is the growth of unwanted vegetation during the fallow period. Such growth of weeds and grasses robs the soil of the moisture and nutrients needed for later crop growth. Moreover, if the weeds are permitted to reach maturity, the seeds are spread by natural means so that the growth of unwanted vegetation is extended both in area and in population.
The conventional method for controlling the growth of unwanted vegetation in fallow land has been to till the soil periodically during the fallow period. This method of vegetative control suffers from numerous drawbacks. Effective tillage control requires repeated passages over the soil, for example up to about five or more such passages during the fallow period. Such repeated operations with conventional fuel consuming equipment is becoming more and more impractical economically. Moreover, such repeated operations require the investment of substantial man-hours. Additionally, soil cultivation opens the soil, thus permitting the excape of soil moisture by evaporation, as well as permitting erosion of the loose soil due to wind.
While a large number of chemical herbicides are now known which are effective in controlling the growth of a wide variety of broadleaf and grassy weeds, their use in a fallow land program generally is precluded for any of a number of reasons. Many such herbicides are not sufficiently long lasting to provide effective control during an entire fallow period. Other herbicides have a substantial carry-over such that desired crops are injured during the growing season following the fallow period.
A herbicide, to be effective in a fallow land program, must meet several requirements:
1. The herbicide should be active both as a preemergence and as a postemergence herbicide. Thus, the herbicide should be active against the weeds which are already growing at the time of crop harvest, for instance those weeds growing in the stubble of the wheat at the time the wheat is harvested. Additionally, the herbicide should be active against the weeds which sprout and come up after the herbicide has been applied.
2. The herbicide should have a broad spectrum of activity. For example, in a fallow wheatland program, a herbicide should be capable of controlling volunteer wheat, in addition to the annual grass and broadleaf weeds which occur in the wheat fields, both immediately after the winter wheat has been harvested, and in the following spring and summer of the fallow period before the soil is prepared and the planting of the next crop of wheat occurs.
3. The herbicide should not be bound to plant residues. For example, in a fallow wheatland program, a herbicide is best applied as a spray over the remaining wheat stubble and wheat straw after the harvest of the crop of wheat, and in order to have greatest utility, the herbicide should permit itself to be washed off of the wheat stubble and wheat straw and other plant residues by the light showers which provide the moisture during the fallow period. By being washed off of the plant residues, the herbicide becomes available for action in the soil where weeds and volunteer wheat sprout and emerge.
4. The herbicide should be stable on soil surfaces and not sensitive to light. Some herbicides are very sensitive to light and therefore, when sprayed over crop residues such as wheat stubble or upon a soil surface and exposed to sunlight, decompose in a very short period of time, a matter of a week or so. The herbicide should be stable on the soil surface so that it is available for action against the later-emerging weeds and volunteer crop such as wheat.
5. The herbicide should be one which is activated with small amounts of rainfall. Because rainfall is so scarce in the regions where a fallow program is practiced, every small amount of moisture is important. If a herbicide is used which requires large amounts of water, for instance an inch or more of rain, to be activated, months could go by before sufficient moisture accumulates to effect activation of the herbicide. In the meantime, weeds and volunteer crop such as wheat could sprout and grow completely out of control. It is therefore important that the herbicide be activated with a small amount of moisture such as one inch or less of rainfall in order to eliminate the weeds and volunteer crop.
6. The activity of the herbicide should not be altered by tillage. This characteristic is important because, depending on the method of practicing the fallow rotation method, the farmer may occasionally wish to cultivate the soil during the fallow year, but it is desirable that the herbicide continue to work to control any weeds which remain or which begin to sprout, which in so doing will remove moisture from the soil. A herbicide which will continue to work after it has been incorporated into the soil in this manner is a desirable product to use.
7. The herbicide should provide approximately a year, that is to say about 10 to 12 months, of weed control in order to be a satisfactory herbicide for use in this fallow land rotation method. This figure is arrived at by considering that a crop such as wheat is usually harvested in July or August, and immediately thereafter the herbicide is applied. To be a satisfactory and suitable herbicide for use in this method, the herbicide should exert its influence on the weeds which were growing at the time the herbicide was applied in late July or in August, and continue to function as a herbicide throughout the remainder of the summer and fall until cold weather comes. Then in the following spring when the earth warms up and the weeds again begin to sprout, along with volunteer wheat and the like, the herbicide should continue to act, and its activity should continue through the spring and summer months up until time to prepare the soil and plant the crop seed for the new crop. For a fallow wheatland program, this period is approximately 10 to 12 months or so from the date at which the herbicide was originally applied.
8. The herbicide should be one which will undergo sufficient degradation to ensure adequate crop tolerance at the end of the fallow period. Thus, the ideal herbicide is one which will last for an extended period of time, say in the vicinity of 10 or 12 months, but, at the end of that time, will have degraded to an extent that it is harmless to the new crop. A herbicide which has not degraded by the end of this long period of time during which the land remains fallow will damage the new crop and decrease the yield thereof, and this is undesirable.
An object of this invention is to provide a method of weed control in fallow land which accomplishes substantially all of the objectives of a chemical fallow program. The method is directed particularly to a fallow wheatland program.